For applying a solid electrolyte to electrochemical devices such as antistatic materials, (galvanic) cells, etc., it is necessary that the solid electrolyte not only has a good ionic conductivity but also is excellent in film forming property, has good storage stability, and can be easily produced. However, a solid electrolyte satisfying all these necessary requirements has not yet been developed.
For example, it is known that the inorganic solid electrolytes shown by Na--.beta.--Al.sub.2 O.sub.3 and Na.sub.1+x Zr.sub.2 P.sub.3-x Si.sub.x O.sub.12 (0.ltoreq.X.ltoreq.3) have a good ion conductivity as described in M.S. Whittingham, Journal of Chemical Physics, Vol. 54, 414 (1971) and A. Clearfield, et al., Solid State Ionics, Vol. 9/10, 895 (1983) but these inorganic solid electrolytes have fatal faults that they have a very weak mechanical strength and are inferior in fabricability into a flexible film.
It is reported the polyethylene oxide (hereinafter, is referred to as PEO) forms a complex functioning as a solid electrolyte with a salt of a metal ion belonging to group Ia or group IIa of the Periodic Table, such as LiCF.sub.3 SO.sub.3, LiI, LiClO.sub.4, NaI, NaCF.sub.3 SO.sub.3, KCF.sub.3 SO.sub.3, etc., and these complexes have a relatively good ion conductivity in P. Vashista et al., Fast Ion Transport in Solid, 131 (1979) and also these complexes have a viscoelasticity and flexibility specific to a polymer, a good workability, and also good storage stability. However, since PEO has a large temperature reliance, although the aforesaid complex may show a good ionic conductivity at a temperature of 60.degree. C. or higher, the ionic conductivity thereof is greatly deteriorated at about room temperature and hence it is difficult to use the aforesaid complexes for products which can be used in a wide temperature range.
Thus, for solving the faults of PEO, various PEO-modified polymers have been proposed. For example, there are a vinylic polymer having a PEO group at the side chain described in D.J. Banister et al., Polymer, Vol. 25, 1600 (1984), a polyphosphagen having a PEO group at the side chain described in D. F. Shriver et al., Journal of American Chemical Society, Vol. 106, 6854 (1984), and a material formed by introducing a low molecular weight PEO group into a part of polysiloxane described in Watanabe et al., Journal of Power Sources, Vol. 20, 327 (1987), etc.
However, these PEO-modified polymers have a low ion conductivity and cannot be practically used.
Thus, for improving the ionic conductivity of polymers at room temperature, materials composed of gels of high molecular compounds carrying an ionic conductor have been recently actively investigated.
For example, JP-B-57-9671 (the term "JP-B" as used herein refers to an "examined Japanese patent publication") discloses a material formed by dissolving polymethyl methacrylate (herein after, is referred to as PMMA) in propylene carbonate (hereinafter, is referred to as PC) and then gelling the solution by heating. However, in order to increasing the ionic conductivity of the aforesaid material to a practically usable level, it is required to use a large amount of PC, which results in greatly reducing the film strength of the material, whereby the material cannot function as a solid electrolyte.
Also, materials using acrylate or methacrylate polymers having various functional groups as a gelling agent for a nonaqueous solvent are disclosed in JP-A-62-20262, JP-A-62-20263, JP-A-62-22375, JP-A-62-22376, JP-A-62-219468, and JP-A-62-219469 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"), but these materials also have the aforesaid problems and materials having both a high ionic conductivity and an excellent film forming property have not yet been developed.
Also, JP-A-63-135477 shows a material composed of a crosslinked high molecular matrix having a PEO group carrying a low molecular weight liquid PEO but the ionic conductivity of the material cannot be over a low value of about 10.sup.-4 s/cm, which is the ionic conductivity of a liquid PEO and the material is unsuitable for use as practical devices.
Furthermore, materials obtained by impregnating a high molecular matrix having a polar group at the side chain with a nonprotonic polar solvent such as PC are disclosed in U.S. Pat. Nos. 4,822,701 and 4,830,939 but in these materials, a large amount of the solvent is required for increasing the ionic conductivity, thereby the problem of greatly reducing the film forming property cannot be solved, and hence the material is also unsuitable for practical use.
Also, for the viewpoint of improving the film forming property, materials obtained by impregnating porous films such as nonwoven fabrics with a high molecule electrolyte are described in JP-A-63-40270 and JP-A-63-102104 but since the ionic conductivity of these materials depends upon the high molecule electrolyte itself, the materials have a fatal fault that the ionic conductivity is very low. Furthermore, a material composed of a porous film having small pore sizes carrying therein an ionic conductor is disclosed in U.S. Pat. No. 4,849,311 but for carrying a liquid ionic conductor, it is necessary to considerably reduce the pore sizes, whereby the interfacial resistance thereof with an electrode material, etc., is greatly increased and hence the material is also unsuitable for practical use.
As described above, conventionally known solid electrolytes cannot meet the whole problems that the ionic conductivity at about room temperature is very low and the film forming property is very inferior or the interfacial resistance with an electrode material, etc., is very large and hence the provision of a solid electrolyte solving the whole problems has been desired.